I. Field of the Invention
The present invention relates generally to power switching devices for controlling electrical and/or electronic appliances, accessories and equipment. More particularly, our invention relates to power switching systems that monitor step changes in the current drawn by at least one of a plurality of devices connected to the system, and, in response, cause other devices connected to the system to be switched on or off. Representative prior art is seen in U.S. Patent class 713, Subclasses 300-324.
II. Description of the Prior Art
Current sensing devices are known in the art for controlling the power supplied by one or more secondary electrical outlets, in response to current changes sensed at a primary outlet that supplies power to a controlling device. For example, power strips are commonly employed for powering electronic appliances, including computer systems, high fidelity and stereo equipment, home theatre installations and the like. Typical power strips are equipped with multiple electrical outlets, and they are designed to be plugged directly into a U.S. standard 120 volt or foreign 240 volt wall outlet that provide power. They are equipped with a plurality of separate, electrical power outlets that provide power to numerous individual electronic components.
In high quality power strips, the output voltage may be conditioned and smoothed by the circuitry. Power spikes and voltage transients and the like are removed by appropriate circuits, including filter networks and the like. Higher quality power strips condition the A/C power distributed to computers and peripherals through their various outlets, and they may electronically shape the output power waveform. Most power strips provide some protection from power surges and transients. A pilot light, usually amber or red in color, provides a visual indication when the strip is properly plugged into an acceptable A/C outlet. A master power switch and one or more switches for controlling individual outlets may be included. High quality power strips that protect equipment from power spikes and voltage transients are ideal for use with computer systems.
Most modern computer installations usually include one or more power strips to provide power to the various components. For example, the main computer unit (i.e., comprising the motherboard and ancillary boards within a suitable cabinet), a printer, and the video monitor are often supplied by a single power strip. Other computer peripherals, such as scanners, external modems, occasionally tape backup units, and the like are also plugged into the master power strip. Where numerous outlets are needed, one or more secondary power strips may be plugged into the master power strip, in master-slave relation.
Relatively recently, small computer systems have adopted several facets of so-called xe2x80x9cgreenxe2x80x9d technology. Newer PC""s (i.e., xe2x80x9cpersonal computerxe2x80x9d) systems, for example, can be instructed to enter a xe2x80x9cpower conservation modexe2x80x9d that xe2x80x9cpowers downxe2x80x9d hard drives and the like after predetermined time intervals. PC systems of this type typically implement green technology through the operating system or BIOS software. Often the xe2x80x9cgreen settingsxe2x80x9d offered by the system BIOS are selectable by the user simply by addressing the CMOS memory options prior to system booting. Green PC""s can power up directly by using the ATX xe2x80x9cpowerxe2x80x9d switch, and they typically power down through software. When the various hard drives in large network file servers, for example, are powered down after periods of monitored inactivity, wear can be reduced, and potentially damaging heat can be reduced. Many modern video monitors include green adaptations that extend their useful lives and conserve power by powering down their cathode ray tubes and deflection circuitry after predetermined periods of inactivity. This powering down process is also an important power conservation and environmental consideration when multiplied by millions of PC""s. It is also mandated by recent EPA regulations.
However, when a newer computer invokes the xe2x80x9cgreenxe2x80x9d power saving mode, many peripherals connected to the power strip are left running. Despite the fact that the system may shut down, the hard drive(s) and/or video, and other peripherals may be left xe2x80x9con,xe2x80x9d thereby generating heat and wasting power. This can occur even in the standby mode. In complex, multi-component computer systems involving expensive audio systems with sub woofers, large tape backups and other accessory items, fifty to one hundred watts of power can be wasted. It would be advantageous if the CPU would also deactivate computer peripherals when the green power cycle is triggered. Further, it would be even more desirable if green computers would thereafter turn on peripherals when CPU activity commences, without requiring the user to tediously manually switch each device on.
There are other disadvantages with power strips. Before using the main on-off switch on a typical power strip, a prudent user must first power down the computer by instructing the operating system to xe2x80x9cshut down.xe2x80x9d Even after the somewhat time consuming shutdown routine is completed, the peripherals remain xe2x80x9con,xe2x80x9d consuming power. Conventional power strips must be manually switched to disable peripherals. But the power strips are often placed on the floor beneath the user""s desk, well away from convenient reach. The main switch is often obscured, if not completely hidden, by a randomly entangled mass of jumbled power cords leading all over the room. What inevitably happens is that the (industrial, business or military) user simply cannot be bothered, and the peripherals are left on.
Conventional power strips are awkward to place properly when used with complex home stereo systems, or with home theater applications. A modern home theater system may comprise a large screen television, a stereo receiver, a VCR, a cable decoder and/or a satellite receiver, a DVD system, a high power audio amplifier unit, one or more cassette or CD players, and several speaker systems, including at least one high powered sub-woofer. When power strips are used for centralized switching, numerous power cords are exposed, and the sight may not be aesthetically pleasing. Further, audio-visual components cannot conveniently be powered up or powered down in unison. Smaller power strips are inadequate because they have too few outlets.
U.S. Pat. No. 4,675,537, issued Jun. 23, 1987, discloses a power strip comprising a primary outlet and a plurality of separate, slave outlets for computer peripherals. The slave outlets can be controlled by condition-responsive sensing. The circuit derives a sensing signal in response to current through one of the outlets. The sensing signal triggers cascaded op-amps that ultimately fire an SCR to energize a downstream relay that controls one or more desired peripherals.
U.S. Pat. No. 5,465,366 derives a power-switching signal by monitoring the video data lines connected to a computer monitor, instead of monitoring input power lines of a device. It can thus control several peripheral devices.
U.S. Pat. No. 5,594,672 shows a software-intensive means of controlling peripherals by monitoring the digital data path between them and the host computer connection.
U.S. Pat. No. 5,821,924 shows a system that derives information from the video data bus to generate peripheral power control signals.
U.S. Pat. No. 5,483,464 illustrates a system using a digital control signal derived from a xe2x80x9cgreenxe2x80x9d computer controlling peripherals.
Bus connections are also monitored in the power saving, peripheral control devices of U.S. Pat. Nos. 5,603,040, 5,477,476 and 5,359,540.
Some prior art power switching systems monitor the incoming A/C current drawn by a monitored device by observing the voltage drop across one or more current-sensing resistors. Such resistors are disposed in series with the incoming power connection, so all of the sampled A/C current that powers the sampled device passes through them. Since the power dissipated by such resistors increases as the square of the voltage developed across them, only small resistive values can be used in practical sensing circuits. As long as relatively high current flows through the resistors, useable voltage signals can be derived across them. When very small currents pass through current sensing resistors of low resistance, the voltage developed across them is very small. When it is necessary to sense these very small voltage signals across the resistors, relatively expensive and sophisticated sensing circuitry is required. Practical limits exist on the ranges of current that can be sensed. A major problem occurs when current drawn by the device or appliance being monitored is very small, i.e., in the order of milliamps or less. The very small signal that results approaches the noise floor. Devices employing current sensing resistors also suffer from a limited range, and cannot ordinarily provide a useful control signal over a relatively wide current range of three or more orders of magnitude (i.e., from milliamps to tens of amps). When switched xe2x80x9con,xe2x80x9d some monitored devices draw significant current, i.e., approximately three or four orders of magnitude greater than the current drawn when xe2x80x9coff.xe2x80x9d Simply stated, if the currents to be measured are very small, for example in the range of a few milliamps, then sensing resistors of large resistive values are required to obtain a sufficient voltage differential (and sufficiently good signal to noise ratio) to represent those currents.
In many applications, the current passing through sensing resistors will increase dramatically when the sensed device assumes different modes of operation. For example, when a typical washing machine changes from a fill cycle, with only its internal solenoids and timer drawing current in the milliamp range, to a wash cycle where the motor is activated, power consumption rises dramatically. Current may rise several orders of magnitude, exceeding ten amps or more. For accurate control signals to be derived by the resistors sensing this current, stability over the entire current range is required. While the resistors must accurately sense lower currents, they must remain stable when subjected to xe2x80x9cI-squared-Rxe2x80x9d losses (and the resultant heat) caused by heavy currents. Proper design becomes awkward and expensive. Ventilation and heat dissipation requirements for the sensing resistors complicates the design and aggravates cost.
Our power control switching circuits are ideal for use with various electronic devices and electrically operated appliances, power tools and the like. For example, embodiments of our circuitry can control computer installations with multiple peripherals, complex audio and home-theatre installations, or electrical appliances. Forms of our invention are ideal for preventing flooding with washing machines or dishwashers by carefully controlling external solenoid valves that supply water to the appliance through flexible hoses and thereby remove the standing water pressure source when the machine is not in use. Another application of our invention relates to dust vacuums, that should be turned on in response to the activation of power routers or table saws. All embodiments of our circuitry employ a sensing subcircuit that monitors power delivered to at least one sensing outlet. Power demands and current characteristics exhibited by the device plugged into the sensed outlet(s) are carefully monitored by the sensing subcircuit that outputs a conditioned DC monitoring signal.
A related control subcircuit driven by the monitoring signal powers suitable relays or semiconductor devices for activating apparatus that is to be switched by our circuitry. Both analog and digital control subcircuits are disclosed. A xe2x80x9cpower stripxe2x80x9d version of our device provides a monitored outlet, to which a computer may be plugged in, and a controlled outlet to which a conventional power strip my be plugged for powering peripherals and accessory components. In this mode, for example, a computer is plugged into our sensed outlet, and a conventional power strip is plugged into our controlled outlet. All the peripherals connected to the strip will be turned on or off when the computer is powered up or powered down. Similarly, complex audio or home video installations controlled by conventional power strips can be activated concurrently by sensing a primary device (i.e., an amplifier, a VCR, or a stereo receiver) plugged into the sensed outlet.
The preferred sensing subcircuits comprise a current sensing network interposed between a source of A.C. power and a sensed electrical outlet, into which a machine or appliance to be monitored is plugged. Thus, all of the power line current delivered to that machine or appliance is passed through the sensing network. The preferred network comprises a transformer having a primary winding connected in parallel with a capacitor and one or more pairs of anti-parallel diodes. A single pair of anti-parallel diodes may be used, or multiple pairs of anti-parallel diodes in series may be employed. The combination of anti-parallel diodes and a transformer winding provide a unique, sensed nonlinear current-voltage transfer function that is further processed by a filter that rectifies and filters the stepped-up transformer output. This monitoring signal is delivered to the control subcircuit.
In each embodiment, the control subcircuit has a solid state switching means that is responsive to the monitoring signal. In the analog variations, the monitoring signal drives a suitable transistor that ultimately controls a relay, or a power transistor where the controlled device/s are operated at a DC potential as in the case of the flood control embodiment of our invention.
In the digital versions, the control subcircuit preferably comprises a microcontroller that executes suitable software steps for dynamically determining the precise points at which the relays or transistors controlling downstream components should be activated or deactivated. In one form of digital control subcircuit, the user may input suitable control points with manual switches that program the microcontroller. In an advanced version of digital control subcircuit, a self-learning program automatically determines future operating parameters in response to parameters determined during initial system setup and component actuation.
Therefore, a basic object of our invention is to provide a highly sensitive current monitoring device for controlling a variety of electrical or electronic loads.
Another basic object is to provide an electronic sensing circuit that can power a plurality of electronic devices, and which derives a signal from a selected one of the devices to control the power to the others.
Another broad object is to provide an extremely sensitive circuit for controlling electronic appliances or devices by sensing small, A/C current changes in a selected appliance or device connected to the circuit.
A still further object is to provide a current sensing device that is extremely sensitive to very small current changes, but which can easily handle much larger currents passing through the system.
Another basic object is to provide a non-linear current sensing network that avoids the limitations of current-sensing resistors.
Yet another object is to avoid the potentially hazardous interposition of sensing-components within the neutral power line. It is a feature of our sensing means that hazardous voltage from the power line is completely isolated from our signal processing circuitry with a transformer circuit that we insert in series with the hot side of the power line. No component, such as a resistor, that has the remotest possibility of going open should ever be inserted in the neutral power line. An open neutral is a death trap. Further, with a sensing component and its subcircuits inserted in the neutral line there exists the remote possibility that the neutral and hot lines could, at some point, be interchanged with again, potentially catastrophic results.
A more specific object of our invention is to provide a flood prevention circuit that monitors dish washers, washing machines or similar appliances, and which disables the water supply lines when appropriate to prevent flooding.
A related object is to provide a current-sensing circuit of the character described that prevents water from flooding or overflowing when a critical hose supplying water to an appliance ruptures when the appliance is not in use.
Yet another specific object of our invention is to provide a highly sensitive, current-sensing circuit of the character described that monitors current changes in monitored devices and derives a corrective control signal therefore.
A still further object is to consistently present the voltage that must be derived for proper low level current sensing. It is a feature of our invention that conventional current sensing resistors are replaced with a network comprising one or more pairs of anti-parallel diodes that shunt the primary of a sensing transformer.
A more basic object is to monitor xe2x80x9cgreenxe2x80x9d computers or equipment, and, in response, to control auxiliary peripherals.
A related object is to provide a controller of the character described that derives useful control voltages from small currents, but which functions ideally even with relatively large currents.
Another basic object is to provide both analog and digital circuits capable of carrying out the above objects.
Another specific object of our invention is to provide a device for controlling home theatre or stereo sound systems by sensing power line current changes in one of a plurality of devices such as a VCR, CD player, DVD player or similar device. It is a feature of our invention that small drops or increases in power line current drawn by a self-timed tape or CD player, for example, are sensed by the invention and used to control other auxiliary components of a high performance audio or video system.
These and other objects and advantages of the present invention, along with features of novelty appurtenant thereto, will appear or become apparent in the course of the following descriptive sections.